CANBERRA (Reuters) - Australia has detected the larvae of khapra beetles in imported nappies sold in supermarkets nationwide, the agriculture ministry said, raising concerns the pest could infest grain storages and disrupt agricultural exports.

The ministry said in a statement on Tuesday it had been working with the importer and retailer of the nappies to trace and treat nappies containing the insect since it was alerted to their detection in New South Wales on September 7.

Agriculture Minister Julie Collins said the beetles, which feed on stored food, making it unusable, hitchhiked to Australia in a shipping container.

"We've managed to track down around 1,500 of the 2,000 cartons (of nappies) but there are still some in circulation," she said in an Australian Broadcasting Corporation (ABC) report on Thursday.

"We want to of course make sure that this doesn't take hold anywhere and we've got them all," Collins said.

Australia is currently free of the khapra beetle, a tiny brown insect up to 3 mm (0.12 inches) long. The maggot-like larvae are a little longer, up to 4.5 mm, golden-brown and hairy.

The agriculture ministry classifies khapra beetles as the biggest pest threat to Australia's A$18 billion ($12 billion) grains industry, saying their establishment in the country would cause trading partners to reject Australian goods, causing huge losses.

Australia is one of the world's biggest exporters of wheat, barley and sorghum.

"This is a pest that would have the same impact as a foot and mouth animal disease outbreak in Australia," said Xavier Martin, president of farm industry group NSW Farmers.

"Governments have to do everything in their power to contain and eradicate this pest, or the damage will be beyond our worst nightmare," he said.

The larvae were found in the brand Little One's Ultra Dry Nappy Pants Walker Size 5, the ministry said, which is only sold by Woolworths, Australia's largest supermarket chain.

Woolworths said it had removed unsold nappies of that brand in that size from shelves and quarantined them. The agriculture ministry said anyone who bought similar nappies should seal them in a bag and call the authorities.

Woolworths said the nappies were supplied by Belgian manufacturer Ontex.

Ontex said in a statement on Thursday it did not know where the larvae had come from but there was no evidence they were introduced when the nappies were being produced.

"Operations at our Eastern Creek manufacturing and warehouse facility (in Sydney) have been suspended until comprehensive checks are completed and we receive confirmation that manufacturing and shipping can safely resume," it added.

Khapra beetles are native to India but have spread through numerous countries in Asia, Africa and Europe, according to the ministry.

($1 = 1.5049 Australian dollars)